John:
The loop amplifier has an on-board 13.8V DC regulator. This has an
overhead of 2.2V, typical, 2.7V worst case. If you use the worst
case for regulator and overhead plus internal voltage drop in
components ahead of the regulator, the MINIMUM DC voltage measured
at the output jack on the loop amplifier is 16.8V.? As a designer,
I have to use the worst case or else risk having some unacceptable
level of failure to operate.
If the supply voltage is below this value, correct operation
cannot be guaranteed. In the best case with 12V, it will sort of
work, but none of the specifications will be met.? Maybe that will
be OK under some conditions, but the internal voltage regulator
will drop out of regulation. The particular regulator used will
"try" to maintain the output voltage at 13.8V, but with only 12V
on the input, it will obviously fail. When these regulators are
operated with lower input voltage than the defined output, they
have a 1 to 2V drop, so the loop amp will see 10 or 11V on the
internal "regulated" supply rail and as I said all performance
data is based on 13.8V, so performance will be degraded.
Jack K8ZOA
On 2/4/2014 9:36 AM, John wrote:
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Jack,
Doug Talley of Pixel told me that the amp would work with
a dedicated 12V power inserter when I contacted him re the
improvements of the 1B loop over my 1A. After sending him
pictures of my late 1A and it's amp, he determined it to
be the then later variant. I guess my question is simple -
will my Pro-1A work with a dedicated 12V negative ground
power inserter for 'emergency' - or portable - use? I have
appropriately sized diecast cases, connectors, etc, and
some 1-10 mH rf chokes rated at several hundred mA, too. I
should have taken him up at the time on his free offer -
at least I'd no. Perhaps, as the designer of the preamp,
Jack, you might comment on the suitability of this. If the
bias will be way off - and the gain suffers - perhaps
we'll look for a 'Plan B'!
John
--- In loopantennas@..., Jack Smith
wrote:
>
> Re battery backup of the Pro-1 loops ...
>
> The power coupler supplies 20V DC (nominal) to the
coax, and is normally
> powered with a 24V AC (RMS) transformer. It is
possible to replace the
> transformer with a floating DC source such as a
battery, but it will
> need around 26V DC. A pair of 12V gel-cell batteries
in series should
> work.
>
> One could try a 12V-120V inverter for battery power,
but from
> theoretical considerations it would need to be a sine
wave or at least a
> modified sine wave inverter. And, there is always the
electrical noise
> issue with inverters.
>
> Jack K8ZOA
>
>
>
